Audio mixing, multiple receiver sources, advice requested

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morfis

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In the photos section it's obvious that some people go to special lengths to have a good audio mixing setup as well as their nice tidy 'shack'.
Several years ago I saw a stereo field mixer for radio type monitoring, it wasn't available via the UK stealers (not that I was in a position to buy one at the time).
I regularly have six receivers (and sometimes quite a few more) active on my desk but using their own speakers or via a PC.

What kind of thing do I need to look for to 'tidy' up the audio outputs - to try and keep the levels similar, enable easy routing for recording etc.? Rackmount/desktop/PC based/controlled solutions are all open for discussion as I really have no idea where to start!

Thanks for any pointers
 

Ubbe

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Audio levels are often difficult as the line out of scanners are dependent of the volume control.
But you could get a cheap audio mixer with enough channels to handle your scanners. Mixers could have mono and stereo input signals and both left and right channel could go to seperate scanners.

On the mixer you have output that you connect to your computer, or amplified speakers, and then you usually have a button that connects any channel to an external output that are supposed to be a echo unit, compressor or something like that. That output can be routed to your computer for recording purposes, or a stand alone voice activated recorder.

You could have that button for all channels enabled to record everything and then release buttons for channels when you only want to record from one scanner. To get the audio back into the mixer you'll need to have duplex set on your computer, so that the audio in also gouse out and back to the mixer, or the mixers general audio output would silence during recording. But there are ways around that or choose a mixer with the necessary features.

If the mixer have USB support you can do more things. It doesn't need to be super low distorsion and be extremly noise free to be used with scanners. Something like a Behringer 1202 costs $100. All these kind of mixers use ground loop isolation transformers so there will be no hum problems.



/Ubbe
 

DeepBlue

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I have been asking folks about this very thing for years now. If we had a simple receive mixer we could plug say 6 or so receiver ext speakers jacks to and have small mixing pots where we could set the levels of each radio to match, that would be good. A simple on off switch to add or subtract individual line inputs would be helpful when we want to isolate a particular "feed". A huge bonus would be to have a stereo option to send certain selectable radios to L or R as needed to help separate them, or to send them on to say a DSP enabled speaker on one output or another. Someone get to work on that will ya. Bob Heil... you out there?

Sean
KB8JNE
 

prcguy

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When using the speaker or earphone jack on a scanner to a mixer you should provide a suitable load resistance to the receiver and I would also use a resistive voltage divider and transformer to isolate all the lines into the mixer. Or you could get one of these designed to take speaker inputs and feed to a single internal powered speaker. I am going to mod this one by adding RCA input connectors.

1.JPG

2.JPG
 

belvdr

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Only problem I have is an SDS200 gives me noise when connected to the headphone jack. I have a Behringer 802USB. This occurs with just the SDS and the 200 connected. Guess I need an isolation transformer but this didn’t occur with the 100 or computer audio.
 

Ubbe

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Someone get to work on that will ya. Bob Heil... you out there?
Exactly what you are asking for are in almost any home studio mixer. Have you looked at a $75 6 channel mixer and read what it can do? You'll have everything there. Most mixers will have a button you hold down on each channel that only selects that single channel and mutes the rest.
When using the speaker or earphone jack on a scanner to a mixer you should provide a suitable load resistance to the receiver and I would also use a resistive voltage divider and transformer to isolate all the lines into the mixer.
Audio mixers already have isolation transformers and each input can be set to either mic or line level and some also have an additional button for each input for a 10dB attenuation. Cheap home studio mixers are incredible advanced for it's price.

/Ubbe
 

belvdr

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Exactly what you are asking for are in almost any home studio mixer. Have you looked at a $75 6 channel mixer and read what it can do? You'll have everything there. Most mixers will have a button you hold down on each channel that only selects that single channel and mutes the rest.
Never seen one do that; only seen the ability to mute a channel.
 

radio3353

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I use this to mix the audio out of my PC and two radios into one speaker...
FIFINE Mixer
But, it handles only 4 inputs so it may not be enough for you. It has been working great for me. I actually have the output feeding a two-port switch 2-port Switch to select between speaker and headphone.
 

Ubbe

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Never seen one do that; only seen the ability to mute a channel.
Try looking for a Solo feature in a mixer.

"Solo, more correctly known as Solo-in-Place (SIP), is an after-fade listen taken from after the pan control as well as the channel fader. It is therefore a stereo signal even on mono channels. The idea is to allow the monitoring of a channel signal when panned to its appropriate position in the stereo image. SIP is usually achieved by monitoring the main mix buss and muting all the channels other than the one you pressed the SIP button on. However, this means that you can't use SIP while mixing because it destroys the mix on the mix buss, muting aux channels as well as main channels."

/Ubbe
 

prcguy

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I don't know of any home studio or affordable mixers for scanner use that have input transformers. An ok input transformer starts around $75 each and goes up from there, that would add $450 to an otherwise $79 mixer. Yes most mixers have selectable mic and line level but you would be feeding it speaker level which is much higher. You should attenuate that by a good 30dB.

The proper way to do this is attenuate the speaker output of the scanner with a resistive voltage divider that provides a good match to the scanner audio amp and attenuates by about 30dB, then run that into a 600 ohm 1:1 line level transformer to the mixer input. That will avoid ground loops, noise, etc and the mixer will run near unity gain.

I could mention I designed an amount of television broadcast studio audio stuff that millions of people watch, but I won't.

Exactly what you are asking for are in almost any home studio mixer. Have you looked at a $75 6 channel mixer and read what it can do? You'll have everything there. Most mixers will have a button you hold down on each channel that only selects that single channel and mutes the rest.

Audio mixers already have isolation transformers and each input can be set to either mic or line level and some also have an additional button for each input for a 10dB attenuation. Cheap home studio mixers are incredible advanced for it's price.

/Ubbe
 

Ubbe

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I don't know of any home studio or affordable mixers for scanner use that have input transformers.
Most of them have that, except the $10 ones. As soon as you see a XLR connector then you can be sure of that there's a transformer involved. They need to have it to power microphones with a phantom connection that uses two balanced audio lines and a third wire that are the DC path for the power to a mic. It's a balun in the mixer that handles that. If you don't have that you'll pick up hum along the cable, the one you often hear from guitars and their amplifiers that have no balanced inputs.

Even Behringers smallest $50 mixer uses balanced isolation transformers.

/Ubbe
 

prcguy

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None of them have it until you get into the multi thousand dollar units for just a few channels. In the US, Mackie and Behringer are probably the most popular for home use and none have input transformers. You won't find them in Allen & Heath or Yamaha or Soundcraft or Tascam or Peavy or anything else in the lower end PA/home studio price range, it simply costs too much. They are not needed for phantom power insertion or even to keep the circuit balanced. I've been inside most mixers I've mentioned and you can easily look up some schematic diagrams and see.


Most of them have that, except the $10 ones. As soon as you see a XLR connector then you can be sure of that there's a transformer involved. They need to have it to power microphones with a phantom connection that uses two balanced audio lines and a third wire that are the DC path for the power to a mic. It's a balun in the mixer that handles that. If you don't have that you'll pick up hum along the cable, the one you often hear from guitars and their amplifiers that have no balanced inputs.

Even Behringers smallest $50 mixer uses balanced isolation transformers.

/Ubbe
 
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chief21

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Ubbe

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None of them have it until you get into the multi thousand dollar units for just a few channels. In the US, Mackie and Behringer are probably the most popular for home use and none have input transformers.
You are absolutly correct. There's no transformer per se but a balanced circuit that have no relation to ground and works as a ground loop isolator.

/Ubbe
 

morfis

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Thanks for the replies so far. Buying some hideous home studio mixer with amultitude of useless twiddly bits is not high on the likely outcomes.

See the link below for a purpose-built device that, unfortunately, is no longer in production - but they can be found "out there". If you can find one, don't hesitate!

Yes, saw it many years ago and paid for one from a well known UK radio stealer...fobbed me off with excuses for NINE months about why it hadn't been delivered and after lengthy discussion got my money back. It would have suited the job nicely.
 

majoco

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I was so intrigued by the RX1602 mixer that I did some more investigation and it more than met my requirements so I ordered one (the last one, it seems!) and it should be here next week. Just one rack unit high is great so not taking up a lot of desk space. One thing I haven't found out yet concerns the configuration of the input jacks - there's two for each channel, one mono that goes into the left channel input with a normal sleeve/tip jack and the stereo jack with a TRS jack - it says its a balanced input on both. What I want to find out is that - does the left channel mono signal find its way into both channels so I can spatially adjust the position of the signal...? We'll have to see. The ability to mute any channel without turning the gain down is good and it would appear that there is a light to indicate that it has been muted. Lots of other good things to play with, although I guess I'm going to be busy making up leads...... :(

Ok, I've read some more - yes the mono signal can be fixed in space. If all else fails, RTFM!
 
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